An axial-flow fan includes a boss portion located at a rotation center portion, and a plurality of blades formed so as to extend from an outer circumferential surface of the boss portion toward a radially outer side. On a downstream side of the boss portion in the axial-flow fan, a flow passing along each of the blades to be blown out and a flow stagnating in a region on an immediately downstream side of the boss portion are mixed, thereby becoming a turbulent flow having a backflow and a vortex. Such a turbulent flow may cause energy loss and increase in noise.
In this case, as the related-art air blower including an axial-flow fan, in Patent Literature 1, there is disclosed a structure in which a conical guide having a diameter expanding toward the downstream side is provided on the downstream side of the axial-flow fan, to thereby suppress separation of the flow to be blown out.
Further, in Patent Literature 2, there is disclosed a configuration in which a guide having an expanding diameter is mounted on a downstream side of an impeller and the guide has a groove formed in an inclined surface thereof.